GNR is right, not only do they need to be the same size but its best with males to have them all neutered, its just a much easier process.
Also make sure that your mom's boss or whatever understand the truth about glider care and wasn't lied to by certain breeders like most people are. And make sure he knows that gliders can't always get together overnight and the introductions make take time.
I've met a few people who have owned gliders much longer than I have but because of those mills they know absolutely nothing about them.